deno/ext/web/10_filereader.js

// Copyright 2018-2025 the Deno authors. MIT license.

// @ts-check
/// <reference no-default-lib="true" />
/// <reference path="../../core/lib.deno_core.d.ts" />
/// <reference path="../../core/internal.d.ts" />
/// <reference path="../webidl/internal.d.ts" />
/// <reference path="../web/internal.d.ts" />
/// <reference path="../../cli/tsc/dts/lib.deno_web.d.ts" />
/// <reference path="./internal.d.ts" />
/// <reference lib="esnext" />

import { primordials } from "ext:core/mod.js";
import { op_encode_binary_string } from "ext:core/ops";
const {
  ArrayPrototypePush,
  ArrayPrototypeReduce,
  FunctionPrototypeCall,
  MapPrototypeGet,
  MapPrototypeSet,
  ObjectDefineProperty,
  ObjectPrototypeIsPrototypeOf,
  queueMicrotask,
  SafeArrayIterator,
  SafeMap,
  Symbol,
  SymbolFor,
  TypedArrayPrototypeSet,
  TypedArrayPrototypeGetBuffer,
  TypedArrayPrototypeGetByteLength,
  TypedArrayPrototypeGetSymbolToStringTag,
  TypeError,
  Uint8Array,
} = primordials;

import * as webidl from "ext:deno_webidl/00_webidl.js";
import { createFilteredInspectProxy } from "ext:deno_console/01_console.js";
import { forgivingBase64Encode } from "./00_infra.js";
import { EventTarget, ProgressEvent } from "./02_event.js";
import { decode, TextDecoder } from "./08_text_encoding.js";
import { parseMimeType } from "./01_mimesniff.js";
import { DOMException } from "./01_dom_exception.js";

const state = Symbol("[[state]]");
const result = Symbol("[[result]]");
const error = Symbol("[[error]]");
const aborted = Symbol("[[aborted]]");
const handlerSymbol = Symbol("eventHandlers");

class FileReader extends EventTarget {
  /** @type {"empty" | "loading" | "done"} */
  [state] = "empty";
  /** @type {null | string | ArrayBuffer} */
  [result] = null;
  /** @type {null | DOMException} */
  [error] = null;
  /** @type {null | {aborted: boolean}} */
  [aborted] = null;

  /**
   * @param {Blob} blob
   * @param {{kind: "ArrayBuffer" | "Text" | "DataUrl" | "BinaryString", encoding?: string}} readtype
   */
  #readOperation(blob, readtype) {
    // 1. If fr's state is "loading", throw an InvalidStateError DOMException.
    if (this[state] === "loading") {
      throw new DOMException(
        "Invalid FileReader state",
        "InvalidStateError",
      );
    }
    // 2. Set fr's state to "loading".
    this[state] = "loading";
    // 3. Set fr's result to null.
    this[result] = null;
    // 4. Set fr's error to null.
    this[error] = null;

    // We set this[aborted] to a new object, and keep track of it in a
    // separate variable, so if a new read operation starts while there are
    // remaining tasks from a previous aborted operation, the new operation
    // will run while the tasks from the previous one are still aborted.
    const abortedState = this[aborted] = { aborted: false };

    // 5. Let stream be the result of calling get stream on blob.
    const stream /*: ReadableStream<ArrayBufferView>*/ = blob.stream();

    // 6. Let reader be the result of getting a reader from stream.
    const reader = stream.getReader();

    // 7. Let bytes be an empty byte sequence.
    /** @type {Uint8Array[]} */
    const chunks = [];

    // 8. Let chunkPromise be the result of reading a chunk from stream with reader.
    let chunkPromise = reader.read();

    // 9. Let isFirstChunk be true.
    let isFirstChunk = true;

    // 10 in parallel while true
    (async () => {
      while (!abortedState.aborted) {
        // 1. Wait for chunkPromise to be fulfilled or rejected.
        try {
          const chunk = await chunkPromise;
          if (abortedState.aborted) return;

          // 2. If chunkPromise is fulfilled, and isFirstChunk is true, queue a task to fire a progress event called loadstart at fr.
          if (isFirstChunk) {
            // TODO(lucacasonato): this is wrong, should be HTML "queue a task"
            queueMicrotask(() => {
              if (abortedState.aborted) return;
              // fire a progress event for loadstart
              const ev = new ProgressEvent("loadstart", {});
              this.dispatchEvent(ev);
            });
          }
          // 3. Set isFirstChunk to false.
          isFirstChunk = false;

          // 4. If chunkPromise is fulfilled with an object whose done property is false
          // and whose value property is a Uint8Array object, run these steps:
          if (
            !chunk.done &&
            TypedArrayPrototypeGetSymbolToStringTag(chunk.value) ===
              "Uint8Array"
          ) {
            ArrayPrototypePush(chunks, chunk.value);

            // TODO(bartlomieju): (only) If roughly 50ms have passed since last progress
            {
              const size = ArrayPrototypeReduce(
                chunks,
                (p, i) => p + TypedArrayPrototypeGetByteLength(i),
                0,
              );
              const ev = new ProgressEvent("progress", {
                loaded: size,
              });
              // TODO(lucacasonato): this is wrong, should be HTML "queue a task"
              queueMicrotask(() => {
                if (abortedState.aborted) return;
                this.dispatchEvent(ev);
              });
            }

            chunkPromise = reader.read();
          } // 5 Otherwise, if chunkPromise is fulfilled with an object whose done property is true, queue a task to run the following steps and abort this algorithm:
          else if (chunk.done === true) {
            // TODO(lucacasonato): this is wrong, should be HTML "queue a task"
            queueMicrotask(() => {
              if (abortedState.aborted) return;
              // 1. Set fr's state to "done".
              this[state] = "done";
              // 2. Let result be the result of package data given bytes, type, blob's type, and encodingName.
              const size = ArrayPrototypeReduce(
                chunks,
                (p, i) => p + TypedArrayPrototypeGetByteLength(i),
                0,
              );
              const bytes = new Uint8Array(size);
              let offs = 0;
              for (let i = 0; i < chunks.length; ++i) {
                const chunk = chunks[i];
                TypedArrayPrototypeSet(bytes, chunk, offs);
                offs += TypedArrayPrototypeGetByteLength(chunk);
              }
              switch (readtype.kind) {
                case "ArrayBuffer": {
                  this[result] = TypedArrayPrototypeGetBuffer(bytes);
                  break;
                }
                case "BinaryString":
                  this[result] = op_encode_binary_string(bytes);
                  break;
                case "Text": {
                  let decoder = undefined;
                  if (readtype.encoding) {
                    try {
                      decoder = new TextDecoder(readtype.encoding);
                    } catch {
                      // don't care about the error
                    }
                  }
                  if (decoder === undefined) {
                    const mimeType = parseMimeType(blob.type);
                    if (mimeType) {
                      const charset = MapPrototypeGet(
                        mimeType.parameters,
                        "charset",
                      );
                      if (charset) {
                        try {
                          decoder = new TextDecoder(charset);
                        } catch {
                          // don't care about the error
                        }
                      }
                    }
                  }
                  if (decoder === undefined) {
                    decoder = new TextDecoder();
                  }
                  this[result] = decode(bytes, decoder.encoding);
                  break;
                }
                case "DataUrl": {
                  const mediaType = blob.type || "application/octet-stream";
                  this[result] = `data:${mediaType};base64,${
                    forgivingBase64Encode(bytes)
                  }`;
                  break;
                }
              }
              // 4.2 Fire a progress event called load at the fr.
              {
                const ev = new ProgressEvent("load", {
                  lengthComputable: true,
                  loaded: size,
                  total: size,
                });
                this.dispatchEvent(ev);
              }

              // 5. If fr's state is not "loading", fire a progress event called loadend at the fr.
              //Note: Event handler for the load or error events could have started another load, if that happens the loadend event for this load is not fired.
              if (this[state] !== "loading") {
                const ev = new ProgressEvent("loadend", {
                  lengthComputable: true,
                  loaded: size,
                  total: size,
                });
                this.dispatchEvent(ev);
              }
            });
            break;
          }
        } catch (err) {
          // TODO(lucacasonato): this is wrong, should be HTML "queue a task"
          queueMicrotask(() => {
            if (abortedState.aborted) return;

            // chunkPromise rejected
            this[state] = "done";
            this[error] = err;

            {
              const ev = new ProgressEvent("error", {});
              this.dispatchEvent(ev);
            }

            //If fr's state is not "loading", fire a progress event called loadend at fr.
            //Note: Event handler for the error event could have started another load, if that happens the loadend event for this load is not fired.
            if (this[state] !== "loading") {
              const ev = new ProgressEvent("loadend", {});
              this.dispatchEvent(ev);
            }
          });
          break;
        }
      }
    })();
  }

  #getEventHandlerFor(name) {
    webidl.assertBranded(this, FileReaderPrototype);

    const maybeMap = this[handlerSymbol];
    if (!maybeMap) return null;

    return MapPrototypeGet(maybeMap, name)?.handler ?? null;
  }

  #setEventHandlerFor(name, value) {
    webidl.assertBranded(this, FileReaderPrototype);

    if (!this[handlerSymbol]) {
      this[handlerSymbol] = new SafeMap();
    }
    let handlerWrapper = MapPrototypeGet(this[handlerSymbol], name);
    if (handlerWrapper) {
      handlerWrapper.handler = value;
    } else {
      handlerWrapper = makeWrappedHandler(value);
      this.addEventListener(name, handlerWrapper);
    }

    MapPrototypeSet(this[handlerSymbol], name, handlerWrapper);
  }

  constructor() {
    super();
    this[webidl.brand] = webidl.brand;
  }

  /** @returns {number} */
  get readyState() {
    webidl.assertBranded(this, FileReaderPrototype);
    switch (this[state]) {
      case "empty":
        return FileReader.EMPTY;
      case "loading":
        return FileReader.LOADING;
      case "done":
        return FileReader.DONE;
      default:
        throw new TypeError("Invalid state");
    }
  }

  get result() {
    webidl.assertBranded(this, FileReaderPrototype);
    return this[result];
  }

  get error() {
    webidl.assertBranded(this, FileReaderPrototype);
    return this[error];
  }

  abort() {
    webidl.assertBranded(this, FileReaderPrototype);
    // If context object's state is "empty" or if context object's state is "done" set context object's result to null and terminate this algorithm.
    if (
      this[state] === "empty" ||
      this[state] === "done"
    ) {
      this[result] = null;
      return;
    }
    // If context object's state is "loading" set context object's state to "done" and set context object's result to null.
    if (this[state] === "loading") {
      this[state] = "done";
      this[result] = null;
    }
    // If there are any tasks from the context object on the file reading task source in an affiliated task queue, then remove those tasks from that task queue.
    // Terminate the algorithm for the read method being processed.
    if (this[aborted] !== null) {
      this[aborted].aborted = true;
    }

    // Fire a progress event called abort at the context object.
    const ev = new ProgressEvent("abort", {});
    this.dispatchEvent(ev);

    // If context object's state is not "loading", fire a progress event called loadend at the context object.
    if (this[state] !== "loading") {
      const ev = new ProgressEvent("loadend", {});
      this.dispatchEvent(ev);
    }
  }

  /** @param {Blob} blob */
  readAsArrayBuffer(blob) {
    webidl.assertBranded(this, FileReaderPrototype);
    const prefix = "Failed to execute 'readAsArrayBuffer' on 'FileReader'";
    webidl.requiredArguments(arguments.length, 1, prefix);
    this.#readOperation(blob, { kind: "ArrayBuffer" });
  }

  /** @param {Blob} blob */
  readAsBinaryString(blob) {
    webidl.assertBranded(this, FileReaderPrototype);
    const prefix = "Failed to execute 'readAsBinaryString' on 'FileReader'";
    webidl.requiredArguments(arguments.length, 1, prefix);
    // alias for readAsArrayBuffer
    this.#readOperation(blob, { kind: "BinaryString" });
  }

  /** @param {Blob} blob */
  readAsDataURL(blob) {
    webidl.assertBranded(this, FileReaderPrototype);
    const prefix = "Failed to execute 'readAsDataURL' on 'FileReader'";
    webidl.requiredArguments(arguments.length, 1, prefix);
    // alias for readAsArrayBuffer
    this.#readOperation(blob, { kind: "DataUrl" });
  }

  /**
   * @param {Blob} blob
   * @param {string} [encoding]
   */
  readAsText(blob, encoding = undefined) {
    webidl.assertBranded(this, FileReaderPrototype);
    const prefix = "Failed to execute 'readAsText' on 'FileReader'";
    webidl.requiredArguments(arguments.length, 1, prefix);
    if (encoding !== undefined) {
      encoding = webidl.converters["DOMString"](encoding, prefix, "Argument 2");
    }
    // alias for readAsArrayBuffer
    this.#readOperation(blob, { kind: "Text", encoding });
  }

  get onerror() {
    return this.#getEventHandlerFor("error");
  }
  set onerror(value) {
    this.#setEventHandlerFor("error", value);
  }

  get onloadstart() {
    return this.#getEventHandlerFor("loadstart");
  }
  set onloadstart(value) {
    this.#setEventHandlerFor("loadstart", value);
  }

  get onload() {
    return this.#getEventHandlerFor("load");
  }
  set onload(value) {
    this.#setEventHandlerFor("load", value);
  }

  get onloadend() {
    return this.#getEventHandlerFor("loadend");
  }
  set onloadend(value) {
    this.#setEventHandlerFor("loadend", value);
  }

  get onprogress() {
    return this.#getEventHandlerFor("progress");
  }
  set onprogress(value) {
    this.#setEventHandlerFor("progress", value);
  }

  get onabort() {
    return this.#getEventHandlerFor("abort");
  }
  set onabort(value) {
    this.#setEventHandlerFor("abort", value);
  }

  [SymbolFor("Deno.privateCustomInspect")](inspect, inspectOptions) {
    return inspect(
      createFilteredInspectProxy({
        object: this,
        evaluate: ObjectPrototypeIsPrototypeOf(FileReaderPrototype, this),
        keys: [
          "error",
          "readyState",
          "result",
        ],
      }),
      inspectOptions,
    );
  }
}

webidl.configureInterface(FileReader);
const FileReaderPrototype = FileReader.prototype;

ObjectDefineProperty(FileReader, "EMPTY", {
  __proto__: null,
  writable: false,
  enumerable: true,
  configurable: false,
  value: 0,
});
ObjectDefineProperty(FileReader, "LOADING", {
  __proto__: null,
  writable: false,
  enumerable: true,
  configurable: false,
  value: 1,
});
ObjectDefineProperty(FileReader, "DONE", {
  __proto__: null,
  writable: false,
  enumerable: true,
  configurable: false,
  value: 2,
});
ObjectDefineProperty(FileReader.prototype, "EMPTY", {
  __proto__: null,
  writable: false,
  enumerable: true,
  configurable: false,
  value: 0,
});
ObjectDefineProperty(FileReader.prototype, "LOADING", {
  __proto__: null,
  writable: false,
  enumerable: true,
  configurable: false,
  value: 1,
});
ObjectDefineProperty(FileReader.prototype, "DONE", {
  __proto__: null,
  writable: false,
  enumerable: true,
  configurable: false,
  value: 2,
});

function makeWrappedHandler(handler) {
  function wrappedHandler(...args) {
    if (typeof wrappedHandler.handler !== "function") {
      return;
    }
    return FunctionPrototypeCall(
      wrappedHandler.handler,
      this,
      ...new SafeArrayIterator(args),
    );
  }
  wrappedHandler.handler = handler;
  return wrappedHandler;
}

export { FileReader };